Skip to Content

Wiki source code of WebObjects with Scala

Version 414.1 by Ravi Mendis on 2010/01/14 23:00
Hide last authors
Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
Ravi Mendis 409.1 3 Scala is a modern language not unlike Groovy.
4 It is said to be more powerful and faster than Groovy or Ruby.
5 This's been the reason for its adoption at sites like Twitter.
Ravi Mendis 195.1 6
Ravi Mendis 409.1 7 Many of its features and paradigms favor multi-threading and concurrency.
Ravi Mendis 413.1 8 It could be said that Scala was designed from the ground up with concurrency in mind.
Ravi Mendis 294.1 9
Ravi Mendis 413.1 10 Some of its features may not be unfamiliar to Objective-C or WebObjects developers.
11 Here's a quick summary:
Ravi Mendis 393.1 12
Ravi Mendis 338.1 13 |= |= Objective-C |= Java |= Scala
14 |= Mutable/Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | Yes
Ravi Mendis 349.1 15 |= Closures | Blocks (//Extension//) | No | Anonymous Functions
Ravi Mendis 338.1 16 |= Static variables | Yes | Yes | No
17 |= Static methods/functions | Yes | Yes | No
18 |= Concurrency | [[Grand Central Dispatch>>http://en.wikipedia.org/wiki/Grand_Central_Dispatch]] (//Extension//)| //Threads// |[[Actors>>http://en.wikipedia.org/wiki/Actor_model]]
19 |= |= Weakly Typed |=--Strongly Typed--|= Strongly Typed
Ravi Mendis 294.1 20
21 Other notable features include:
22
Ravi Mendis 338.1 23 |= |= Objective-C |= Java |= Scala
24 |= Parametered methods | Yes //e.g: addObject: to~:// | No | Yes //e.g: add(object= ,to=)//
25 |= Class composition | Categories | Interfaces | Traits
Ravi Mendis 294.1 26
Ravi Mendis 338.1 27 A fuller description of Scala can be found [[here>>http://en.wikipedia.org/wiki/Scala_(programming_language)]].
28
Ravi Mendis 195.1 29 === Why Use Scala? ===
30
Ravi Mendis 411.1 31 With Web 2.0, building concurrent WebObjects applications is a must.
Ravi Mendis 401.1 32 Developing and maintaining a concurrent or multi-threaded WebObjects application can be challenging.
Ravi Mendis 195.1 33
Ravi Mendis 401.1 34 The lack of static variables means that Scala is inherently thread-safe.
35 It has concurrency that is effectively built-in to the language in the form of Actors.
Ravi Mendis 318.1 36
Ravi Mendis 401.1 37 So for WebObjects developers, Scala offers itself as a powerful, safe and easy-to-use solution for concurrent applications.
38
Ravi Mendis 294.1 39 === Can WebObjects be Programmed In Scala? ===
Ravi Mendis 195.1 40
Ravi Mendis 288.1 41 Yes. It is very simple.
Ravi Mendis 318.1 42 Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
Ravi Mendis 195.1 43
Ravi Mendis 294.1 44 = WebObjects In Scala =
Ravi Mendis 195.1 45
Ravi Mendis 294.1 46 The following highlights some of the differences between Java and Scala in WebObjects:
Ravi Mendis 195.1 47
Ravi Mendis 294.1 48 == EOs in Scala ==
49
Ravi Mendis 318.1 50 === Thread-Safe Shared Vars ===
Ravi Mendis 294.1 51
Ravi Mendis 318.1 52 Scala doesn't have static variables or methods. However, a class can have a //Companion Object// that will allow you to achieve something equivalent to static variables.
53 One of the advantages of this approach is that it is **thread-safe**, so you don't have to worry about synchronizing access to these fields in a concurrent application.
Ravi Mendis 294.1 54
Ravi Mendis 359.1 55 The following is an example of the use of a //Companion Object// for Talent in Scala instead of Talent static fields in Java.
Ravi Mendis 294.1 56
Ravi Mendis 355.1 57 Java:
58
Ravi Mendis 393.1 59 {{code value="java"}}
Ravi Mendis 308.1 60
Ravi Mendis 369.1 61 public class _Talent extends EOGenericRecord {
Ravi Mendis 294.1 62 public static final String ENTITY_NAME = "Talent";
63
64 {{/code}}
65
Ravi Mendis 355.1 66 Scala:
Ravi Mendis 294.1 67
68 {{code}}
69
Ravi Mendis 369.1 70 object Talent extends EOGenericRecord {
Ravi Mendis 294.1 71 val ENTITY_NAME = "Talent"
72
73 {{/code}}
74
Ravi Mendis 318.1 75 ==== Compacted imports ====
Ravi Mendis 308.1 76
Ravi Mendis 318.1 77 Two lines in Java are compacted into one in Scala.
Ravi Mendis 308.1 78
Ravi Mendis 294.1 79 In Java:
80
Ravi Mendis 393.1 81 {{code value="java"}}
Ravi Mendis 294.1 82
83 import com.webobjects.eocontrol.EOGenericRecord;
84 import com.webobjects.eocontrol.EORelationshipManipulation;
85
86 {{/code}}
87
88 In Scala:
89
90 {{code}}
91
92 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
93
94 {{/code}}
95
96 == WOComponents in Scala ==
97
98 ==== Compact Constructors ====
99
100 Scala allows for simpler use of multi-valued constructors than Java.
101
102 In Java:
103
Ravi Mendis 393.1 104 {{code value="java"}}
Ravi Mendis 294.1 105
106 public class MenuHeader extends WOComponent {
107
108 public MenuHeader(WOContext aContext) {
109 super(aContext);
110 }
111
112 {{/code}}
113
114 In Scala:
115
116 {{code}}
117
Ravi Mendis 312.1 118 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
Ravi Mendis 294.1 119
120 {{/code}}
121
122 ==== Simplified Exception Handling ====
123
124 Scala doesn't force you to catch exceptions unlike in Java.
Ravi Mendis 395.1 125 In addition, the syntax employs Scala's very powerful pattern matching to handle different exceptions.
Ravi Mendis 294.1 126
127 In Java:
128
Ravi Mendis 393.1 129 {{code value="java"}}
Ravi Mendis 294.1 130
131 try {
132 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
133 epi.setNextPage(context().page());
134 nextPage = (WOComponent) epi;
135 } catch (IllegalArgumentException e) {
136 ErrorPageInterface epf = D2W.factory().errorPage(session());
137 epf.setMessage(e.toString());
138 epf.setNextPage(context().page());
139 nextPage = (WOComponent) epf;
140 }
141
142 {{/code}}
143
144 In Scala:
145
146 {{code}}
147
148 try {
149 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
150 epi.setNextPage(context.page)
151 nextPage = epi.asInstanceOf[WOComponent]
152 } catch {
153 case e: IllegalArgumentException => {
154 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
155 epf.setMessage(e.toString)
156 epf.setNextPage(context.page)
157 nextPage = epf.asInstanceOf[WOComponent]
158 }
159 }
160
161 {{/code}}
162
Ravi Mendis 381.1 163 ==== Scala Annotations vs. Generic Accessors ====
164
Ravi Mendis 385.1 165 An example of accessing variables in WebObjects with the following languages:
Ravi Mendis 381.1 166
Ravi Mendis 385.1 167 |= |= Objective-C |= Java |= Scala
168 |= getter | ##object name## | ##object.name()## | ##object.name##
169 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
Ravi Mendis 381.1 170
Ravi Mendis 385.1 171 Of course in Java, we may generate WebObjects classes with "get" methods as well in order to stick to convention.
172 In scala there is an additional convenience we may use to produce "get" and "set" methods in addition to the default Scala accessors - Scala Annotations.
173
174 E.g, in Main.scala we annotate our component keys with ##@BeanProperty## to automatically create public "set" and "get" methods.
175 These variables can then be accessed via //KVC//.
176
177 {{code}}
178
179 @BeanProperty var username = new String()
180 @BeanProperty var password = new String()
181 @BeanProperty var isAssistantCheckboxVisible = false
182
183 {{/code}}
184
Ravi Mendis 353.1 185 == How to Use Scala Collections with EOF ==
Ravi Mendis 351.1 186
187 One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily ##List##, ##Map##, ##Seq## and ##Set##.
188 Employing these instead of ##NSArray## and ##NSDictionary## in WebObjects/EOF may be challenging.
189
190 But one may modify the EO templates to produce API such as:
191
192 {{code}}
193
194 def movies: NSArray[EOGenericRecord] = {
195 storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[EOGenericRecord]]
196 }
197
198 def moviesList: List[EOGenericRecord] = {
199 movies.objects.toList
200 }
201
202 {{/code}}
203
Ravi Mendis 318.1 204 == How to Add Scala to a WO Project ==
Ravi Mendis 308.1 205
206 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
207
Ravi Mendis 338.1 208 {{note title="Note"}}
Ravi Mendis 318.1 209
210 This is for Eclipse/WOLips IDE
211
212 {{/note}}
213
Ravi Mendis 290.1 214 == WO Scala Example ==
215
Ravi Mendis 353.1 216 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
Ravi Mendis 292.1 217 All the EO logic and WO components are in Scala.
Ravi Mendis 318.1 218 Only the Application class is Java.
Ravi Mendis 292.1 219
Ravi Mendis 353.1 220 It is based on the D2W Movies example.
221
Ravi Mendis 290.1 222 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 223
224 === Setup ===
225
Ravi Mendis 318.1 226 1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
Ravi Mendis 353.1 227 1. Install and start the OpenBase OBMovies database.
Ravi Mendis 294.1 228 1. Right-click on Application.java and run as a WOApplication (as usual).
229
Ravi Mendis 318.1 230 ==== EO Templates ====
Ravi Mendis 294.1 231
232 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
233
Ravi Mendis 357.1 234 1. Point to the local [[Scala versions>>http://wiki.objectstyle.org/confluence/display/WOL/EOGenerator+Templates+and+Additions]] of the .eotemplate files for ##Entity## and ##//Entity//##
Ravi Mendis 294.1 235 1. Change the File Names Extension to "scala"
Ravi Mendis 367.1 236 1. In Destination Paths set the Superclass Package (e.g: base)
Ravi Mendis 294.1 237 1. Uncheck Java under Options
Ravi Mendis 385.1 238
239 == How to Build & Deploy a WebObjects Scala Project with Ant ==
240
241 1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
Ravi Mendis 393.1 242 1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
243 1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
244 1. Run from the project directory: ##sudo ant clean install##